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Results for “computational modeling”

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At least 991 records · Page 55Linked to original sources
PubMed1995

New computational models of the respiratory oscillator in mammals.

Understanding how respiratory oscillations are generated and controlled in the mammalian brainstem requires synthesis of neural function at cellular, synaptic, and network levels. Modeling the respiratory network has entered a new era where simulations incorporating complex cellular properties and network interactions exhibited by respiratory neurons are possible. Given the complexity and unknowns of the real system, there are obvious limitations of the modeling in its present form. Nevertheless, if we are to produce neurobiologically satisfying, mechanistic explanations that synthesize cellular and network phenomena, the modeling approach outlined here should have distinct advantages. The approach allows a close interaction between experimental and computational studies, and will enable simulations with increasing neurobiological realism as additional experimental data becomes available. The modeling summarized here represents the initial stages of establishing a computational framework for storing information about neuron and network properties, and for exploring complex dynamical properties in ways not possible experimentally.

Animals↗
PubMed2005

Brain-behaviour relationships in latent inhibition: a computational model.

In a series of studies, we applied a neural network to study the neural bases of latent inhibition. We first designed a model able to handle behavioral data and then we investigated whether structures and neural elements in the brain were able to carry out the operations described by network. We demonstrated that the network was able to describe many of the behavioral properties of LI, and elucidate the effects of several manipulations of the dopaminergic system, the hippocampus, and the nucleus accumbens on LI, as well as some of the positive symptoms of schizophrenia. The results support the idea that a 'conceptual nervous system' can be successfully used to relate brain and behavior.

Animals↗
PubMed1999

Computer models for masked hearing experiments with beluga whales (Delphinapterus leucas).

Environmental assessments of manmade noise and its effects on marine mammals need to address the question of how noise interferes with animal vocalizations. Seeking the answer with animal experiments is very time consuming, costly, and often infeasible. This article examines the possibility of estimating results with software models. A matched filter, spectrogram cross-correlation, critical band cross-correlation, and a back-propagation neural network detected a beluga vocalization in three types of ocean noise. Performance was compared to masked hearing experiments with a beluga whale [C. Erbe and D. M. Farmer, Deep-Sea Res. II 45, 1373-1388 (1998)]. The artificial neural network simulated the animal data most closely and raised confidence in its ability to predict the interference of a variety of noise source with a variety of vocalizations.

Animals↗
PubMed1999

Computational model of the serotonergic modulation of sensory neurons in Aplysia.

Serotonergic modulation of the sensory neurons that mediate the gill- and tail-withdrawal reflexes of Aplysia is a useful model system for studies of neuronal plasticity that contributes to learning and memory. The effects of serotonin (5-HT) are mediated, in part, via two protein kinases (protein kinase A, PKA, and protein kinase C, PKC), which in turn, modulate at least four membrane currents, including a S ("serotonin-sensitive") K(+) current (I(K, S)), a steeply voltage-dependent K(+) current (I(K-V)), a slow component of the Ca(2+)-activated K(+) current (I(K,Ca-S)), and a L-type Ca(2+) current (I(Ca-L)). The present study investigated how the modulation of these currents altered the spike duration and excitability of sensory neurons and examined the relative contributions of PKA- and PKC-mediated effects to the actions of 5-HT. A Hodgkin-Huxley type model was developed that described the ionic conductances in the somata of sensory neurons. The descriptions of these currents and their modulation were based largely on voltage-clamp data from sensory neurons. Simulations were preformed with the program SNNAP (Simulator for Neural Networks and Action Potentials). The model was sufficient to replicate empirical data that describes the membrane currents, action potential waveform and excitability as well as their modulation by application of 5-HT, increased levels of adenosine cyclic monophosphate or application of active phorbol esters. In the model, modulation of I(K-V) by PKC played a dominate role in 5-HT-induced spike broadening, whereas the concurrent modulation of I(K,S) and I(K,Ca-S) by PKA primarily accounted for 5-HT-induced increases in excitability. Finally, simulations indicated that a PKC-induced increase in excitability resulted from decreases of I(K,S) and I(K,Ca-S), which was likely the indirect result of cross-talk between the PKC and PKA systems. The results provide several predictions that warrant additional experimental investigation and illustrate the importance of considering indirect as well as direct effects of modulatory agents on the modulation of membrane currents.

Action Potentials↗
PubMed1999

Computer modeling of visual impairment caused by intraocular lens misalignment.

PURPOSE: To evaluate a computer program to modulate the visual impairment caused by intraocular lens (IOL) misalignment and visualize results obtained by numerical calculations. SETTING: Department of Ophthalmology, Medical Faculty of Charles University, Prague, Czech Republic. METHODS: The optic imagery of a Landolt circle was calculated using a ray-tracing computer program. Visual aberrations resulting from a decentered and/or tilted IOL were studied using this program and compared with theoretical calculations. RESULTS: The IOL decentration and/or tilt shifted the postoperative refractive errors toward myopia and astigmatism (oblique). The combination of IOL decentration and tilt produced a refractive error that depended on the relationship between the geometrical axes of the decentration and tilt. The refractive error can be enhanced or diminished depending on the relationship of these axes. CONCLUSIONS: These findings verify the results calculated by paraxial vergence equations. A ray-tracing program simulated the optic imagery for various kinds of IOL misalignment and IOL optic properties.

Astigmatism↗
PubMed1989

A computer model to dynamically simulate protein folding: studies with crambin.

The current work describes a simplified representation of protein structure with uses in the simulation of protein folding. The model assumes that a protein can be represented by a freely rotating rigid chain with a single atom approximating the effect of each side chain. Potentials describing the attraction or repulsion between different types of amino acids are determined directly from the distribution of amino acids in the database of known protein structures. The optimization technique of simulated annealing has been used to dynamically sample the conformations available to this simple model, allowing the protein to evolve from an extended, random coil into a compact globular structure. Many characteristics expected of true proteins, such as the sequence-dependent formation of secondary structure, the partitioning of hydrophobic residues, and specific disulfide pairing, are reproduced by the simulation, suggesting the model may accurately simulate the folding process.

Computer Simulation↗
PubMed1982

A computer model of the left ventricular epicardial surface for quantification of jeopardized myocardium.

A computer program has been developed that can be used to quantify the extent of probable myocardial damage which will result from occlusion of a jeopardized coronary vessel. The program, used as an adjunct to coronary arteriography, permits calculation of an area of an arbitrary segment of the left ventricular epicardial surface. This segmental area, when expressed as a fraction of the total LV epicardial area, is a measure of the myocardial mass supplied by a specific coronary arterial vessel. The computer program has been extended to include graphic, three-dimensional simulation of different views of the left ventricular epicardium.

Computers↗
PubMed1992

Computer model of ultrasonic hyperthermia and ablation for ocular tumors using B-mode data.

Computer simulations have been conducted to examine hyperthermia and ablation for treating ocular tumors. An interactive software package has been implemented that permits relevant tissue dimensions to be determined from B-mode data. This package also permits interactive beam positioning, and it provides image displays depicting computed absorbed doses and temperature rises. Results are presented showing how hyperthermia temperature patterns are influenced by beam position, beam geometry and frequency. Images showing ablative temperature rises at various time intervals are also presented. For hyperthermia, geometric models of beam profiles showed that a non-uniform beam pattern (with a central low-intensity region) can produce more uniform heating of small ocular tumors than a beam with a uniform intensity profile. For a given tumor, the uniformity of hyperthermia temperatures was found to be a function of frequency, with 4.75 MHz providing reasonably uniform results for typical tumor heights (near 7 mm). For ablation, diffraction computations were employed to calculate beam intensity profiles; results show an initially rapid rise in temperature levels with subsequent, slower heating beyond the -3-dB limits of the focal volume. The model is now being refined, and additional phenomena, including nonlinear propagation, will be incorporated.

Body Temperature↗
PubMed1988

Computer modeling of thoracic response to blast.

Primary blast injury affects the gas-containing structures of the body. Damage to the lungs with resultant respiratory insufficiency and arterial embolization of air from alveolar pulmonary venous fistulae is the predominant cause of morbidity and mortality following high-level blast exposure. In an effort to generate a widely applicable damage-risk criterion for thoracic injury from blast we are developing a complex computer finite element model (FEM) of the thorax. Taking an engineering approach, a horizontal cross-section of the thorax is divided into small discrete units (finite elements) of homogeneous structure. The necessary physical properties (density, bulk modulus, etc.) are then determined for each element. Specifying the material constants and geometry of the elements, the computer can load the surface of the structure with some force-time function (blast pressure-time history) and calculate the resultant physical events such as displacement, compression, stress, strain, etc. Computer predictions of pressure wave phenomena in the lung parenchyma are compared with trans-bronchially measured pressures in blast-exposed animals. The model should prove useful in assessing the risk of blast injury in diverse overpressure environments and may give insight into pathophysiologic mechanisms and strategies for protection.

Animals↗
PubMedDate not supplied

Computational models of collective foraging.

In this paper the behaviour of a bee colony is modelled as society of communicating agents acting in parallel and synchronising their behaviour. Two computational approaches for defining the agents behaviour are introduced and compared. Their common features as well as the complementary aspects making them suitable for merging together into a more complex model.

Animals↗